Exposure to marijuana isn’t associated with significant changes in brain morphology in either older or younger subjects, according to a pair of new studies.

As reported by NORML, in the first study, researchers from the University of Pennsylvania, Perelman School of Medicine compared brain scans of occasional (one to two times per week) and frequent (more than three times per week) marijuana consumers versus nonusers. Occasional marijuana use was defined as using it ones or twice a week, whereas frequent consumption was considered to be the use of the plant more than three times a week. Subjects were between 14 and 22 years of age.

Investigators reported: “There were no significant differences by cannabis group in global or regional brain volumes, cortical thickness, or gray matter density, and no significant group by age interactions were found. Follow-up analyses indicated that values of structural neuroimaging measures by cannabis group were similar across regions, and any differences among groups were likely of a small magnitude.”

They concluded, “In sum, structural brain metrics were largely similar among adolescent and young adult cannabis users and non-users.”

The findings appear in the journal Neuropsychopharmacology.

In the second study, researchers from the University of Colorado at Boulder compared magnetic resonance imaging (MRI) scans in 28 cannabis users over the age of 60 versus matched controls. Cannabis consuming participants, on average, had used marijuana weekly for 24 years.

Authors reported that long-term cannabis exposure “does not have a widespread impact on overall cortical volumes while controlling for age, despite over two decades of regular cannabis use on average. This is in contrast to the large, widespread effects of alcohol on cortical volumes that might be expected to negatively impact cognitive performance.” Researchers also reported “no significant differences between groups” with regard to cognitive performance.

They concluded: “The current study was able to explore cannabis use in a novel older adult population that has seen recent dramatic increases in cannabis use while controlling for likely confounding variables (e.g., alcohol use). The participants in this study were generally healthy and highly educated, and it is in this context that cannabis use showed limited effects on brain structural measures or cognitive performance.”

The findings appear in the journal Psychiatry Research: Neuroimaging.

The studies’ conclusions are similar to those of prior trials finding no significant long-term changes in brain structure attributable to cannabis exposure.

The full text of the study, “Cannabis use in youth is associated with limited alterations in brain structure,” appears in the journal Neuropsychopharmacology. The full text of the study, “Preliminary results from a pilot study examining brain structure in older adult cannabis users and nonusers,” appears in Psychiatry Research: Neuroimaging.

A separate study found that After adjusting for potential confounders, the cumulative use of cannabis — even among young people — is not associated with either a significant or long-term adverse impact on intelligence quotient

“In the largest longitudinal examination of marijuana use and IQ change, … we find little evidence to suggest that adolescent marijuana use has a direct effect on intellectual decline. … [T]he lack of a dose-response relationship, and an absence of meaningful differences between discordant siblings lead us to conclude that the deficits observed in marijuana users are attributable to confounding factors that influence both substance initiation and IQ rather than a neurotoxic effect of marijuana”, states the study.